Mad Lab Mini geoslime is water based and if it is left out, it will dry out eventually. The best way to keep Mad Lab Mini slime hydrated is to store it in the Mad Lab Minis vial it came in – or another airtight container. But if you are playing for hours & your slime is starting to dry out, you can try to rehydrate with water by kneading in a drop at a time. The amount will depend on how long it has been left out, but the key is to add only a small amount at a time… if you add too much it will fall apart! There are many online articles & videos suggesting alternative methods you could try as well… we can’t guarantee results with any of these, but we think it can be fun trying different things. We’d also love to hear from you if you find a magic ingredient other than water that works really well… please share via our customer support page!